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The idglobal attribute defines an identifier (ID) which must be unique in the whole document. Its purpose is to identify the element when linking (using a fragment identifier), scripting, or styling (with CSS).

The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

This attribute's value is an opaque string: this means that web authors should not rely on it to convey human-readable information (although having your IDs somewhat human-readable can be useful for code comprehension, e.g. consider ticket-18659 versus r45tgfe-freds&$@).

id's value must not contain whitespace (spaces, tabs etc.). Browsers treat non-conforming IDs that contain whitespace as if the whitespace is part of the ID. In contrast to the class attribute, which allows space-separated values, elements can only have one single ID value.

Note: Using characters except ASCII letters, digits, '_', '-' and '.' may cause compatibility problems, as they weren't allowed in HTML 4. Though this restriction has been lifted in HTML5, an ID should start with a letter for compatibility.